Practice ball



Dec. 18, 1962 J. A. DILLON, JR 3,069,l 70

PRACTICE BALL Filed Feb. 4, 1959 IN V EN TOR. J06: 4. 0/7/00, Jr.

HTTORNEY 3,069,170 Patented Dec. 18, 1962 3,069,170 PRACTICE BALL John A. Dillon, Jr., Coleman, Mich., assignor to The Dow Chemical Company, Midland, Mich., a corporation of Delaware Filed Feb. 4, 1959, Ser. No. 791,073

3 Claims. (Cl. 273-199) This invention relates to practice balls for use in connection with such sports as golf and the like.

' The conventional practice golf balls are of two general varieties; one of which is a cotton ball, the other a plastic shell type.

The ordinary cotton practice ball consists of a loose, disordered agglomeration of textile fibers that are confined by means of a woven fabric cover. Although such balls are generally made of cotton, they may also be fabricated from other fibers, including synthetic materials. The assembly of the cover and the fibrous filler give a product of roughly spherical shape which may be used as a practice ball for golf or for equivalent purposes.

Such a product, however, has some severe and pronounced disadvantages. Thus, on repeated use, the cover may become worn and discolored or the ball itself may tend to lose its desired shape. Due to the highly absorbent nature of most of the filler materials used in the construction of the cotton ball, it frequently is quite easily wet when being utilized on wet terrain, as in damp grass. This may also contribute to its loss of shape, or cause it to gain weight so as to become quite unsatisfactory for further use. In some cases, as is apparent, a change of weight may be accompanied by an undersirable and disadvantageous change in the location of the center of gravity of the ball. This may give rise to erroneous indications to the user. In addition, the useful life of the cotton type practice ball is oftentimes of relatively short duration.

The plastic shell type of practice golf ball usually consists of two generally perforated, flexible plastic hemispheres that are circumferentially joined edge-to-edge so as to result in a hollow, flexible plastic sphere which, ordinarily, is left within the perforated surface. The plastic shell balls are oftentimes an improvement over the cotton type of practice ball, since the former will not assimilate large quantities of moisture. However, the structure of the plastic shell ball exhibits a decided tendency to crack under repeated physical impact, as from the head of a golf club. Thus, the joint between the two hemispheres, which is a weak portion of the structure, is prone to fail under impact. Obviously, this renders the practice ball of no further practical value.

This invention has as a principal objective, the manufacture of improved practice balls.

A further object of this invention is the production of a practice golf or similar ball which comprises a synthetic material which possesses to a high degree the properties most desired in practice golf, or the like, ball construction.

A further object of this invention is to provide a practice golf, or the like, ball that will not absorb or tend to accumulate water so as to thereby change its weight.

A further object of this invention is to provide a practice golf, or the like, ball with an appearance that closely resembles that of a golf ball used in normal play.

Another object is to provide practice balls for various sports, for example, golf, tennis, baseball, squash, and the like.

These and other objects are accomplishedand many significant benefits and advantages achieved in and by a practice ball in accordance with the present invention which comprises a generally spherical structure that has been formed from, and is comprised of, expanded or foamed and cellular polyethylene or the like non-aromatic hydrocarbon polymer (such as polypropylene or a copolymer of ethylene and propylene).

Practice balls prepared in accordance with this invention are a significant advance over the usual commercially available practice balls. They are resistant to repeated impact, have low moisture pick-up, low dirt retention and excellent weight uniformity.

Further features and yet additional advantages and benefits of the articles of the present invention will be more fully manifest in the ensuing description and specification, taken in connection with the accompanying drawing, wherein:

FIGURE 1 shows a view of the completed ball;

FIGURE 2, a cross-sectional view, illustrating the cellular nature of the article;

FIGURE 3 shows a practice golf ball;

FIGURE 4 shows a practice baseball; and

FIGURE 5 shows a practice tennis ball.

There is illustrated in FIGURE 1 a ball made in accordance with the present invention, indicated generally by the reference numeral 10. The ball 10 is fabricated from expanded or foamed polyethylene, polypropylene, or copolymer of ethylene and propylene so as to contain a plurality of included cells or voids 12, defined by cell Walls 11, as depicted in the cross-sectional view of FIG- URE 2. The surface 13 of the ball 10 may be relatively smooth, as shown in FIGURE 1, as when it is formed by means of a sharp-bladed cutting instrument.

If desired, however, various surface configurations and patterns may be provided on the surface of the ball to achieve particular effects. Thus, as is shown in FIG- URE 3, small cup-like surface recesses 14, or the like depressions may be cut or impressed in the surface of the practice ball to correspond precisely to the surface usually found on ordinary golf balls. Or, in other varieties or balls intended to simulate other articles, raised portions may be left to simulate the seams of a ball, such as a baseball, as illustrated by the reproduced seams 15 on the surface of the ball in FIGURE 4. Likewise, as demonstrated in FIGURE 5, grooves 16 (in the manner of a tennis ball seam) may be provided in the practice tennis ball of FIGURE 5. In a similar manner, surfaces of squash, cricket, table tennis, and the like balls may be simulated.

The preferred size of the cell, or void 12 of the expanded polyethylene, polypropylene or copolymers of ethylene and propylene or the like balls'of the present invention, may vary, depending upon the application intended therefor. Generally, it is desirable to employ material having cell sizes from about 1 micron to about of an inchfor such balls as intended to be employed for golfing practice. In the larger practice balls, however, as in practice baseballs, tennis balls, and the like, relatively larger cell sizes up to about /8 of an inch or so may be employed.

The invention is not limited to employment of a closed cell structure in the expanded polyolefin from which the ball is fabricated, although such cells are generally more advantageous to employ for most balls. This is due to the lower moisture absorption of such a cell arrangement. In certain instances, however, open cell, sponge or free-blown ce-ll forms may be employed, desipite the fact that for most usual applications they may be less desirable.

The polymers of ethylene that may be expanded and employed for fabrication of the balls of the present invention may, for example, be identical with or similar to those which may be obtained by polymerizing ethylene in a basic aqueou medium and in the presence of polymerization-favoring quantities of oxygen under relatively high pressures in excess of 500 or 1,000 atmospheres at temperatures between 150 and 275 C. Or, if desired, the polymers of ethylene and propylene, or copolymers thereof, may be the essentially linear and unbranched polymers ordinarily having greater molecular weights which may be obtained, amongst other ways, under relatively low pressures of l to l atmospheres'using such catalysts to polymerize the ethylene as mixtures of strong reducing agents and compounds of group IV-B, V-B and VI-B metals of the periodic system; chromium oxide on silicated alumina; hexavalent molybdenum compounds; and charcoal supported nickel-cobalt.

The expanded, cellular non-aromatic hydrocarbon polymer stock used or provided for fabrication and construction of the balls of the present invention such as those illustrated, for example, in FIGURES 1, 2, 3, 4, and 5, may be prepared by contacting molten polyethylene or linear polypropylene with a low boiling liquid, such as, for example: tetrafluoromethane, dichlorodifiuoro-methane, pentane, and the like; then intimately mixing the two components under pressure; followed by cooling of said mixture to a temperature from 3 to centigrade degrees above the solidification temperature of the mixture; then subsequently exposing the mixture rapidly to a lower pressure, such as atmospheric pressure. By altering the conditions, as, for example, temperature, pressure and proportions of the polymer and blowing agent, foams may be prepared having densities varying from about 1.5 to about 50 pounds or so per cubic foot.

Foams having general utility for the manufacture of practice balls have density margins from about 1.5 pounds per cubic foot to about 30 pounds per cubic foot. However, an advantageous range of density is from about 1.6 to about pounds per cubic foot. An even more advantageous range for most purpose is from about 2 to about 10 pounds per cubic foot. Balls made from foams having higher densities may be employed in locations where the playing area permits and indications obtainable in use of balls made therewith tend to require less interpretation than does the information acquired through use of the lighter balls. Usually, however, balls fabricated from a lower density material having a greater volume-to-mass ratio are more desirable when space limitations are of major concern.

Practice balls in accordance with the invention may readily be prepared by releasing the hereinbefore mixture of polymer and blowing agent into a mold cavity which has a generally spherical shape. A mold having two matching hemispherical cavities and, of course, an inlet sprue may be employed. Usually it is desirable to maintain a mold temperature of about 30 C. The interior surface of the mold may be patterned to give varying surfaces which may be desired. It may be noted that practice balls prepared using such a foam molding technique have surfaces that are less irregular, as no foam cells are sectioned in the forming operation.

Suitable practice balls may also be formed by carefully carving by hand employing a sharp bladed instrument, as a knife edge or the like, a sphere from a solid mass prepared as hereinbefore described. In order to obtain most advantageous performance from the finished practice ball when such a fabricating technique is used, slow and careful cutting is required with constant checking of dimensions to assure a finished surface that is free from undesired irregularities.

Mechanical cutting and shaping means for the carving may be employed, such as rapidly revolving, sharp bladed milling cutters. Alternatively, the work may be revolved and a sharp bladed tool held against the foam stock to shape it as is done on a conventional wood lathe.

In an analogous manner, a hot wire or the like may be used to cut foamed polyolefin stock. Practice balls may be formed by hand-carving with a hot wire or, when the wire is shaped in the form of a semicircle, the polyolefin foam stock may be rotated against the concave side of said wire and a generally spherical ball will result. Minor imperfections, such as cut-off points, may then be manually removed.

A convenient method of heating a wire to be used for cutting thermoplastic foam material is to pass an electrical current therethrough which is of a sufiicient magnitude to cause the temperature of the wire to rise appreciably above the melting point of foam and remain below the range of thermal decomposition of the thermoplastic material.

The use of a hot wire to form such a sphere results in a smoother surface 13 than when a sharp cutting instrument is employed. A melting of the cell walls 11 takes place using the hot wire method and the melted polymer tends to become spread across the freshly cut surface 13, thus stiffening the severed edges.

A further method of preparing practice balls is to cut a rough pre-form from the expanded polyolefin foam stock having slightly larger dimension than required in the finished ball and then employing this pre-form to prepare a finished spherical practice ball therefrom. This is done by inserting the pre-form into a split spherical mold heated to a temperature from about 10 to centigrade degrees above the melting point of the foam stock; then removing the thereby produced ball when sufiicient heat has been applied to the foam to form the desired spherical object without causing the entire foam structure to collapse. The temperature of the mold and residence time in the mold will vary according to the type of polymer foam used, size of cell in the foam and bulk of the pre-form employed. If the size of the pre-form is close to that of the mold, less foam melting will be required than if the pre-form is excessively large.

Molding of the foam produces a still smoother surface 13 on the practice ball 10 than the hereinbefore described methods. The smoothness of the surface 13 may be controlled by the size of pre-form employed. A preform considerably larger than the mold will tend to give a smoother surface 13 on molding than will one which is only slightly larger than the mold.

As the surface of the molded practice ball 10 conforms readily to the inner surface of the mold, various surface ornamentations such as, for example, those shown in FIGURES 3, 4 and 5, may be impressed on practice balls by use of molds having a suitably formed surface.

In preparing a practice golf ball, the diameter of the resultant sphere usually should be about 1.680 inches. A practice baseball usually should be formed to give a sphere having a circumference between 9 and 9% inches; a practice tennis ball between 2 /2 and 2 /3 inches in diameter; a practice soft ball between 11% and 12% inches in circumference; a practice hard ball about 1% inches, plus or minus of an inch; a practice squash ball about 1% inches in diameter; a practice table tennis ball between 4 /2 and 4% inches in circumference.

The following examples are illustrative of the present invention, but are not to be considered limitative of the scope thereof.

EXAMPLE I A block of cellular polyethylene having an apparent density of about 2.67 pounds per cubic foot was shaped into several spheres by means of manually carving with a sharp razor blade. A slicing motion was used to obtain effective cutting action of the blade. The diameter of each resultant sphere was about 1.68 inches. The cellular polyethylene carvings were spherical in shape, having surfaces that were free from irregularities other than those resulting from the cellular structure of the raw material itself.

One of the resulting practice balls was tested in the following manner. Three tees were placed in the ground. On tee number 1 was placed a conventional, commercially procured cotton ball. On tee number 2 was placed a commercially obtained plastic shell ball. On the third tee was placed the cellular poyethyene ball of the present invention. Each ball was struck to about the same degree of impact in numerical order ofi? the tees by a full, hard stroke of a number one wood (i.e., a driver). The balls were replaced on their respective tees and the procedure repeated a number of times. The number of strokes each ball received and the results of the testing are shown in the following Table I.

Table I Tee Strokes Condition Cotton Ball 1 38 cover torn, dirty. Plastic Shell Ball 2 67 seam split, dirty. Cellular Polyethylene Ball.-. 3 250 no apparent change,

slight arcumulation of dirt.

EXAMPLE II An electrically heated hairpin of copper wire having a diameter of about 0.13 inch was used to manually carve a cellular polyethylene sphere. Cutting was accomplished by placing the wire against the foam stock and slowly forcing it therethrough. The resultant ball had a diameter of about 1.68 inches. Table II shows the results of tests performed as described in Example I employing the ball formed by the hot wire.

A cube of cellular polyethylene was cut having the edge 7 dimension approximately inch greater than the diameter of the spherical practice golf ball required. Right pyramids, the shorter sides of each of which formed right angles and had lengths which were approximately onethird the diameter of the finished ball, were cut from each corner of the cube and discarded. The resulting polyhedron Was then compressed in a split spherical mold, heated to 120 C. for 20 minutes, cooled to 30 C. The resulting ball was then removed from the mold. A small amount of flash was trimmed from the spherical molding. The thereby-obtained ball product was subjected to the same testing and comparison outlined in Example I, the results of which are given in Table III.

Table 111 Tee Strokes Condition Cotton Ball 1 45 cover torn, dirty. Plastic Shell Ball 2 78 seam split, dirty. C ellular Polyethylene Ball- 3 250 no damage, little dirt.

From the above examples, the superiority of the invention over the conventional practice golf balls may readily be seen.

In a similar manner to the foregoing examples, other practice balls, such as, for example, balls for tennis, squash, baseball, soft ball, and table tennis, may be prepared having high uniformity, similar high resistance to impact, dirt retention and low moisture pick up. Such balls may advantageously be prepared from polyethylene, polypropylene, and copolymers of ethylene and propylene.

Use of the products of the present invention in the presence of moisture, as with a practice golf ball in the early morning when the grass is covered by dew, oflers no problem of compaction, shapelessness, dirt accumulalation, unbalance, or change of weight.

While various embodiments of the invention have been illustrated and described, it is to be fully understood that the invention is not limited thereto, but is capable of such modifications and further embodiments as may occur to those skilled in the art without departation from its intended spirit and scope.

What is claimed is:

1. As an article of manufacture, a practice golf ball, of spherical shape having a diameter of from about 1.6 to about 1.8 inches, said ball comprising polyolefin foam having a density of from about 1.5 to about 50 pounds per cubic foot, said polyolefin comprising a polymer of non-aromatic hydrocarbon monoolefin of from 2 to 3 carbon atoms.

2. The practice ball of claim 1, wherein the polyolefin is polyethylene having a density of from about 1.6 to about 15 pounds per cubic foot.

3. The practice ball of claim 1, wherein the polyolefin is polytheylene having a density of from about 2 to about 10 pounds per cubic foot.

References Cited in the file of this patent UNITED STATES PATENTS 1,021,520 Handloser et al. Mar. 26, 1912 1,602,725 Travers Oct. 12, 1926 1,981,959 Landreth Nov. 27, 1934 2,525,965 Smith Oct. 17, 1950 2,525,966 Smith et al. Oct. 17, 1950 2,670,528 Brunberg Mar. 2, 1954 2,743,931 -Pooley et al May 1, 1956 2,753,599 Pietraszek et al July 10, 1956 2,948,664 Rubens et al. Aug. 9, 1960 FOREIGN PATENTS 524,063 Great Britain July 29, 1940 753,259 Great Britain July 18, 1956 783,324 Great Britain Sept. 18, 1957 

